Separation of azeotropic mixtures

Abstract

A process for separating a liquid mixture of at least two components A and B which form an azeotrope with one another, optionally together with further components, comprises (i) distilling the mixture to be separated in the presence of an auxiliary H which with each of the two components A and B forms a binary azeotrope AH or BH which has a boiling point lower than that of H, and (ii) isolating an A,H-containing fraction which is depleted in B compared to the mixture to be separated and a B,H-containing fraction which is depleted in A compared to the mixture to be separated.

We claim:  
     
         1 . A process for separating a liquid mixture of at least two components A and B which form an azeotrope with one another, optionally together with further components, which comprises 
 i) distilling the mixture to be separated in the presence of an auxiliary H which with each of the two components A and B forms a binary azeotrope AH or BH which has a boiling point lower than that of H, and    ii) isolating an A,H-containing fraction which is depleted in B compared to the mixture to be separated and a B,H-containing fraction which is depleted in A compared to the mixture to be separated.    
     
     
         2 . A process as claimed in  claim 1 , wherein the auxiliary H is additionally able to form a ternary azeotrope with the components A and B.  
     
     
         3 . A process as claimed in  claim 1 , wherein the mixture to be separated is introduced continuously into a column for the distillation.  
     
     
         4 . A process as claimed in  claim 3 , wherein at least part of the auxiliary is introduced into the column together with the mixture to be separated.  
     
     
         5 . A process as claimed in  claim 3 , wherein at least part of the auxiliary H is introduced at the top and/or in the upper region of the column.  
     
     
         6 . A process as claimed in  claim 5 , wherein the auxiliary H is obtained as bottom product and is recirculated at least partly to the top and/or into the upper region of the column.  
     
     
         7 . A process as claimed in  claim 3 , wherein the A,H-containing fraction is taken off at a point above the feed point for the mixture to be separated and the B,H-containing fraction is taken off at a point below the feed point for the mixture to be separated.  
     
     
         8 . A process as claimed in  claim 5 , wherein the mass flow of the auxiliary H introduced is from 0.5 to 15 times the mass flow of the mixture to be separated, based on the part different from H.  
     
     
         9 . A process as claimed in  claim 1 , wherein the binary azeotrope AH and/or BH is a heteroazeotrope.  
     
     
         10 . A process as claimed in  claim 9 , wherein the liquid or liquefied A,H-containing and/or B,H-containing fraction is subjected to a phase separation to give an A-rich or B-rich phase and an H-rich phase and the H-rich phase is returned to the column.  
     
     
         11 . A process as claimed in  claim 1 , wherein the mixture to be separated is a mixture comprising a first component selected from among chlorinated hydrocarbons and monocyclic C 6 -C 10 -aromatics and a second component selected from among C 3 -C 8 -alkanols and the auxiliary used is water.  
     
     
         12 . A process as claimed in  claim 11 , wherein the chlorinated hydrocarbon is perchloroethylene and the alkanol is n-butanol and the mixture optionally further comprises butyl chloride.  
     
     
         13 . A process as claimed in  claim 12 , wherein the liquefied n-butanol/water fraction is subjected to a phase separation to give an n-butanol-rich phase and a water-rich phase and the n-butanol-rich phase is separated by distillation into a fraction enriched in n-butanol and a fraction depleted in n-butanol.  
     
     
         14 . A process as claimed in  claim 12 , wherein a fraction which comprises butyl chloride and water and is largely free of perchloroethylene and n-butanol is additionally obtained as lowest-boiling fraction.  
     
     
         15 . A process as claimed in  claim 11 , wherein the auxiliary H further comprises a base.